When a press machine, a machine tool, construction equipement, a ship, an aircraft, an unattended conveyor an unattended storagehouse or the like is controlled in a centralized manner, many sensors for detecting the respective conditions of the elements of such machine and many actuators for controlling the respective conditions of the elements of the machine are required. The number of these sensors and actuators, for example, reaches 3,000 or more in the case of a press machine and much more in other devices.
Conventionally, a centralized control system which controls such a machine in a centralized manner is constructed such that many such sensors and actuators are connected to a main controller which collects the outputs of the sensors and controls the actuators in accordance with signals from the main controller.
In such conventional centralized control system, the number of lines which connect the main controller and the sensors and actuators is large and the structure of the input/output of the main controller is very complicated as the respective numbers of sensors and actuators are large.
An arrangement is proposed in which a plurality of nodes are connected in series, each node being connected to one or more sensors and actuators, the nodes being connected in a ring via a main controller which outputs signals to the respective nodes for controlling purposes. In such arrangement, basically, the main controller is required to have only signal input and output lines and the respective nodes are only required to connect signal input and output lines. Thus, the number of lines is greatly reduced.
However, in the arrangment where the nodes are connected in series, it is a problem how to ensure the simultaneous collection of the respective outputs of the sensors and the simultaneous respective control of the actuators. For example, if an arrangement is considered in which addresses are allocated to corresponding nodes, which are then controlled in accordance with those addresses, the problem is a time delay due to this address processing, and the simultaneous collection of the respective outputs of the sensors and of the simultaneous control of the actuators cannot be ensured.
The inventors have proposed a series control system which identifies the respective nodes according to the sequence of connection of the respective nodes to thereby render the address processing useless, eliminates the time delay due to the address processing, and greatly simplifies the node structure while discarding the concept of allocating addresses to the respective node although a structure to connect the respective nodes in series is employed.
This arrangement operates such that the respective nodes sequentially add the output signals from those nodes to the signals from the upstream nodes, sequentially extract signals from the upstream nodes to those nodes and outputs them to the actuators in those node in accordance with a predetermined rule. In this case, each node does not need any address, and no address processing is required, so that a time delay in each node includes a very small one required for timing only to thereby greatly simplify the structure of the nodes.
FIG. 11 shows one example of the structure of the whole series controller, mentioned above.
In FIG. 11, reference numeral 10 denotes a machine controller as the above controller which controls an object machine synthetically; 2-1 to 2-n, sensors or actuators disposed in the respective sections of the machine; 30, a central controller (main controller) disposed as the central processing unit at the machine controller 10; 4-1 to 4-n, peripheral controllers (node controllers) disposed as peripheral processing devices at the correponding sensors or actuators 2-1 to 2-n to supply various data (sensor data or actuator control data) between the corresponding sensors or actuators and the central controller 30. In the illustrated series control system, the central controller 30 as the central processing unit and the peripheral controllers 4-1 to 4-n as the peripheral processing devices are connected in series in a ring via a signal line 50 as shown in FIG. 11.
FIG. 12 illustrates one example of protocols of signals S0-Sn which are transmitted between the controllers 30 and 4-1 to 4-n in the series controller.
In this example, the respective signals S0-Sn each include a "train of data" which comprises sensor data indicative of a respective one of the outputs of the sensors or control data indicative of the control contents to control the actuation of a respective one of the actuators; a "start code" disposed directly before the train of data and indicative of the head of train of data with a predetermined logical structure of a plurality of bits (for example, 8 bits); a "stop code" disposed directly after the train of data and indicative of the trailing end of the train of data with a predetermined logical structure (different from that of the start code); and an "error check code" generated in each of the controllers for detection of the occurance of an error among ports (the controllers) and added as a code signal of a predetermined number of bits (for example, of bits) directly after the stop code. The respective controllers 30 and 4-1 to 4-n recognize the presence of the data (the train of data) in accordance with the detection of the start code and stop code and the presence of error generation in accordance with a check on the "error check code" (using to CRC check or veritical/horizontal parity check or the like).
It is true that such series controller ensure achieving the transmission/reception of data and error check effectively by employing a signal having a protocol mentioned above as a signal to be transmitted between the respective controllers. However, when the signal line is broken, for example between the peripheral controller 4-1 and 4-2 of FIG. 11, the signal S1 and subsequent signals are not transmitted to the respective controllers, so that the data cannot be transmitted and received. Therefore, the position of the broken line is required at once to be found and the line is required to be repaired so as to recover the normal state.
In this case, if the central controller 30 supervises the signals during the operation time, it can determine surely whether line breakage has developed, but it cannot get information on where the line breakage developed such as "line breakage developed on a signal line corresponding to the signal S1 (before the peripheral controller 4-2)", so that repair or the like cannot rapidly be performed, disadvantageously.
The present invention derives from the contemplation of these situations. It is an object of the present invention to provide a device for detecting the position of broken line in a series controller which device is capable of getting correct information on the position of line breakage when it occurs to thereby allow the broken line to be repaired rapidly.